Front element moves in and out when zooming, so a UV filter must be used to seal the front.

I ordered this lens after finding that my kit (28 2.8, 50 1.4, 28-105 3.5-4.5 and 70-200 4L) didn't have anything wide enough for my 10D. I love my 70-200 and was therefore expecting similar performance from this lens.

Well, it's better than I expected. Images have the same look as the 70-200 - slightly warm, excellent contrast and sharp sharp sharp. I find it amazing that Canon can get this performance out of such an extreme design.

If (when really) I eventually get a 1.3x or full-fame camera I expect that the true beauty of this lens will show itself, but for now I'm satisfied with its exceptional performance and I'm now really considering selling my 28 2.8 and even my 28-105. When I go to paid shoots it's going to be this and the 70-200 in a pocket and I'll be covered. This, the 50 1.4 and the 70-200 is really all you need with a 10D for professional coverage and image quality.

A joy to use in every way, really. If you have a 10D just get it. Don't think about it any more, just get it.

Internal focus and zoom, metal components, large rubber zoom and focus rings. Half the price of the 2.8 version, small and light enough to carry around for long periods of time, excellent value.

Cons:

Why is the tripod ring so #*!$!@ expensive? Doesn't really need it but it would be nice to have it more balanced on the tripod.

With the possible exception of my 10D, I've not come closer to feelings of love for an inanimate object in my short life. What's not to like? There have been many reviews here, so I'll just say that I wish everything I bought was as well thought out, constructed and performed as well as this. With the high ISO performance of the latest DSLRs, the F4 is more viable. Though it would be nice to have 2.8, this is an excellent compromise and I'd buy it again in a heartbeat.

It does attract a lot of attention in casual use, but when using it to shoot sports or any other situation where people are expecting photographers, they just assume you're a professional. It's rather amusing.

My one nitpick is that the tripod collar is exceedingly expensive - enough so that I'm just going to wait until I get the 300 F4L as the collar comes with that lens and fits this one. I would really like it to use for landscape photography on a tripod.

It is what it is. I got mine last week and can't say anything bad about it. The build quality is totally fine. The plastic is very high quality, textured stuff and a casual look would suggest that it was metal. I'm not planning on hammering nails with it, anyways. The focus ring on mine feels smoother, less plasticky and more damped than my 50 F1.4, and is by no means of poor quality. The DOF scale is actually useful, too, unlike the 50, which only has F22. The autofocus is extremely buzzy, but then there isn't a lot of focus travel with it, either. It's not really an issue, especially if you're a landscaper and can just drop it into MF mode and go nuts.

Optics? This is where it shines. No problems whatsoever. Sharp from corner to corner on the 1.6x crop. No discernable distortion. It's about as wide as I need on the 10D, and as it's a normal lens with the crop factor, it's great as a walkaround.

If you're in doubt about your need for a lens at this focal length, it can be picked up really cheaply and you'll have top-quality glass at little cost. It'll still be a good addition even if you decide to go 17-40 F4L in the future, as the extra stop is sometimes worth it.